1. Field of Invention
The present invention relates to an optical device and a fabricating method thereof. More specifically, the present invention relates to an image sensor and a fabricating method thereof.
2. Description of Related Art
With the popularization of multimedia, various digital image devices have been developed sequentially. An image sensor being a key component of digital image devices has gained significant importance. The function of an image sensor is to transform image information into electrical signals. Image sensors may be categorized into various types, such as charge coupled device image sensors (CCD image sensor), complementary metal oxide semiconductor image sensors (CMOS image sensor) etc. Due to low cost, low power consumption, random access ability and high integration ability, CMOS image sensors are widely used in popular products, such as camera phone and web-cameras.
FIG. 1 illustrates a schematic cross-sectional view of a conventional CMOS image sensor. Referring to FIG. 1, sensing devices 120 of a conventional CMOS image sensor 100 are formed in a substrate 102, wherein the sensing devices 120 comprise a plurality of photo diodes with p-n junctions formed in the substrate 102. More specifically, the sensing devices 120 formed in the substrate 102 comprise n-type doped regions, p-type doped regions and p-n junctions formed between the n-type doped regions and the p-type doped regions. An interconnection layer 104 comprising a plurality of metal interconnections and a plurality of inter-dielectric layers (not shown in figure) therebetween are formed on the substrate 102. An electrical signal representing image information received by the sensing devices 120 is transmitted to a printed circuit board (PCB) 110 via the metal interconnections, in order to process the received image information. A plurality of color filters 132 arranged in an area array are disposed on the interconnection layer 104, wherein each color filter 132 is aligned with one of the sensing devices 120, respectively. In addition, a plurality of micro-lenses 130 performing the function of condensing light, are disposed over the color filters 132. Furthermore, a glass substrate 134, disposed above the micro-lenses 130, is connected to the interconnection layer 104 by a spacer 150.
The light 140, which passes through the micro-lenses 130, the color filters 132 and the interconnection layer 104, is received by the sensing devices 120. Therefore, the layout of the metal interconnections (not shown in figure) should not overlap an area above the sensing devices 120 in order to improve the sensitivity of the sensing devices 120. However, this makes the layout design complicated.
Furthermore, the light 140 coming from the outside environment after passing through the interconnection layer 104 is degraded because it is partially shielded (absorbed or reflected) by the inter-dielectric layers of the interconnection layer 104, and thereby the sensitivity of the sensing devices 120 is affected significantly.
As described above, the sensing devices 120 receive the light 140 coming from the outside environment after it passes through the interconnection layer 104. Therefore, the conventional CMOS image sensor 100 has a low fill rate and contrast ratio (CR). Furthermore, the yield rate of the conventional CMOS image sensor 100 is also low.